The present invention relates to valves that are both opened and closed with a snap-action. More particularly, the invention relates to bi-stable snap action for valves or their actuators where the retaining force governing the snap action of the valve is adjustable.
Certain types of valves have severely attenuated lives if they are not fully open or fully closed. Severe wear occurs when the valve is in an intermediate position for a sustained period. Thus, there has been a recognized need for a repeatable, stable snap action in valves.
Several types of bi-stable mechanisms previously disclosed in other patents are discussed below, including Belleville spring washers, canted biasing springs with angularly varying lines of action, magnetically-biased valves, and spring-biased ball latches or collet latches.
Belleville spring washers with ratios of initial axial offset (from flat)-to-thickness greater than the squareroot of 2 have the unusual property of decreasing load with increased deflection for deflections beyond a certain critical deflection value. If a biasing spring for a valve or valve actuator is predeflected (preloaded) to or beyond that critical value, then whenever the actuating load exceeds that corresponding force, the biasing spring resistance collapses and a snap-through action occurs. Belleville springs, however, can only withstand small deflections. While it may appear that using a stack of similar Belleville springs in series will permit obtaining larger deflections, the random critical load values from an assortment of superficially identical Belleville springs make the obtaining of predictable behavior essentially impossible. This is because the stronger springs will exert higher forces than can be resisted by the weaker springs when the series is preloaded to near its nominal critical value. As a result, the weaker springs fully collapse sequentially, thereby unloading the stronger springs to below their critical values. For this reason, as well as the high friction associated with a large stack of Bellville springs, the mechanism using multiple Belleville springs shown in FIG. 1 of Kinzbach U.S. Pat. No. 2,655,935 is unworkable as an effective snap-through device. Practical short-deflection valves can successfully apply single Belleville springs in snap-through configurations for valve biasing (e.g., U.S. Pat. Nos. 3,892,258, 4,133,186, and 5,255,711). Thus, Belleville springs do not appear to offer snap-action potential for valves requiring more than minimal displacement or relief valves based on rotating ball valves.
The use of canted biasing springs with angularly-varying lines of action is another means by which snap action has been sought. When a coil compression spring has one end anchored against translation but has both ends free to rotate about axes normal to a plane defined by the spring axis and the axis of translation of the non-fixed end of the spring, then a snap-through action can be obtained. This snap-through occurs for angles between the spring axis and the axis of translation of the non-fixed spring end exceeding a critical magnitude. FIG. 7 of Kinzbach (U.S. Pat. No. 2,655,935) displays a relief valve based upon this type of spring biasing with multiple springs. The Kinzbach arrangement attempts to provide snap action both for opening and closing, but its travel is limited so that it is always biased to move to reseat the valve. This limit on travel is such that the springs do not travel past the point where their thrust direction reverses, so that the open position of the valve is not stable.
Turner et al. (U.S. Pat. No. 4,026,314) discloses a single-spring biased valve. This valve does travel past the point where the direction of spring bias on the valve is reversed. For this arrangement, the Turner valve must be manually reset by forcing the spring to move back to its original position with the spring bias direction restored to its original orientation. The primary drawback to the application of canted springs for snap through action in a valve is the relatively large radial spatial requirements for housing such an arrangement. The spatial requirements are increased if stronger springs or more travel are required.
Magnetically biased valves are another means by which controllable snap action for valves has been sought. A magnet with its poles oriented to attract a piece of magnetic material exhibits an attractive force which increases with its approach to that piece; the converse is true for increasing separation. This relatively rapid loss of attractive force with increasing separation distance or gain of attractive force with decreasing separation is well suited to providing snap-action behavior. This phenomena has been used to retain a spherical plug on a seat for an emergency shutoff valve disclosed in Japanese Patent 09042505 A. The spherical plug is not strongly held, so that it can be readily displaced by transverse or angular accelerations such as those which might occur in a strong earthquake. The sphere is able to roll slightly downhill after displacement, where it may be held displaced by gravity and/or its attraction to a peripherally placed housing wall. However, the unseating motion for this device is not well-controlled, so that reseating can accidentally occur, depending on the character of the shaking of the valve.
Another type of magnetically latched valve is shown in Mueller et al. (U.S. Pat. No. 3,013,531). This device is a snap acting reversing valve used in a grease gun. A piston is driven by the fluid controlled by the snap acting valve. Toward either end of the stroke of that piston, a lost-motion coupling connected to that piston by a spring on each side is caused to overcome magnetic biasing force on the actively attracted one of a pair of similar, opposed valve poppets so that the valve is shifted. This device relies on a lost-motion coupling between the driving piston and the valving, and the magnetic attraction is directly between the valve sealing member and its seat.
Other means used to provide snap action are spring-biased latches or collet latches in valves. Tausch et al. (U.S. Pat. No. 3,749,119) discloses a valve reopening operator sleeve retained in either an upper position or a lower position by the engagement of annular latch grooves with an annular garter spring. Although closure of the main valve is not impacted by the sleeve, the reopening of the valve is. Shifting of an independent inner sleeve, mounted within the valve reopening sleeve, downwardly to a first position permits closing an activator valve at the upper end of the reopening sleeve. The closure of the activator valve permits the reopening sleeve to be pumped downwardly from its upper position to its lower position to force open the main valve. The reopening sleeve is disengaged from its lower position by independent upward movement of the main control sleeve. The main valve and the activator valve are both flapper valves and are both spring-biased closed. The garter spring does not cause snap action in this application, but rather serves as a releasable retainer on a secondary operator.
Raulins (U.S. Pat. No. 3,070,119), Dickens (U.S. Pat. No. 3,126,908), and Peters (U.S. Pat. No. 3,889,751) all disclose valves using latches for snap action.
Raulins has a latch based on spring-loaded balls which act directly on the sealing poppet of the valve to provide snap action closure only. The sealing poppet of the valve is loaded by pressure drop across an integral internal flow bean. This load is supported by an annular array of balls which are spring-biased inwardly to engage a shoulder on the sealing poppet. The biasing load on the balls is provided by a very large axial force from an axially-acting coil spring bearing on a conically tapered ball support ring. The snap action is only in one direction and is actuated by forces applied to the sealing member, rather than an independent actuation mechanism.
The Peters apparatus is similar to that of Raulins, but the latch arrangements differ. Peters permits the sealing plug to move a limited amount prior to closing and uses axially translating balls that shift from one groove to another to release. Raulins permits substantially no sealing plug movement prior to latch release and does not use axially translating balls. The Dickens apparatus relies on an actuator with either a collet latch or ball latch released by movement to a disengagement groove under flow forces. A lost motion mechanism is required to link the actuator to the valve in order to accommodate the movement without affecting valve position. A very high axial bias force on the latch mechanism is required. The valve closing and opening require high flows to occur, so that reliable snap action is not a certainty with this device.
Watkins (U.S. Pat. No. 4,160,484) discloses a flapper-type valve in which the flapper is biased to be normally closed, but is held open by a tube latched by a collet mechanism which releases at a predetermined load. The valve functions independently of the tube when the tube is not in position to paralyze the valve. The collet serves only to retain the tube in position and the latch does not provide for snap action.
Not one of the described valves has a stable snap action in both directions (i.e., opening and closing the valve).
There is a need for a stable bidirectional snap action valve that will be more reliable and provide longer operational service.
The invention contemplates a simple, inexpensive device for solving the problems and disadvantages of the prior approaches discussed above. The present invention provides a mechanism for a quick, automatically-operating, snap acting opening and closing valve which is resistant to wear.
One aspect of the present invention is a valve having a bidirectional, bi-stable snap action mechanism for opening and closing.
Another aspect of the present invention is a linear valve having a pair of detents spaced along the length of the valve actuator, wherein a biasing force engages either one or the other detent upon the opening or closing of the valve.
Yet another aspect of the present invention is a ball valve having a number of detents on the ball, wherein a biasing detenting force engages different detents for the open and closed positions of the valve.
Still yet another aspect of the present invention is a ball valve having a number of detents along the length of the valve actuator, wherein a biasing detenting force engages different detents for the open and closed positions of the valve.
Another aspect of the present invention is a valve actuator having a force responsive piston; an actuator housing with a biasing means mounted therein; and a reciprocally movable actuator rod attached to and driven by the force responsive piston and having two detents axially spaced to correspond to a distance between a first and second actuator end position, wherein the biasing means engages a first detent when the actuator is in its first end position and a second detent when said actuator is in its second end position, such that an actuating force applied by the piston that is sufficient to disengage the biasing means and the detent is sufficient to move the actuator fully to the other end position.
The foregoing has outlined rather broadly several aspects of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and the specific embodiment disclosed might be readily utilized as a basis for modifying or redesigning the structures for carrying out the same purposes as the invention. It should be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims.